In RAN1#80bis, Korean government adopts LTE and D2D features for Korean public safety. It was proposed that Rel-13 LTE D2D should be designed with no change to Rel-12 physical layer sidelink signals and channels for public safety. This does not preclude essential enhancements that reuse Rel-12 physical sidelink signals and channels if they have no impact to keep Rel-13 standardization timeline. The intention is to avoid hardware changes in the Rel-13 eD2D in supporting Network-to-UE (user equipment) relay and out-of-coverage/partial coverage discovery. The limitations of no hardware changes implies the constraint of eD2D system design in the following ways:                No change of Rel-12 physical layer channels structures;        No change of Rel-12 physical layer modulation and coding schemes;        No change of Rel-12 physical layer procedures for SA and data; and        No change of Rel-12 physical layer measurements.        
In Rel-13 eD2D, Network-to-UE relay requires reference measurement in support of relay node selection. Rel-12 defines Sidelink Reference Signal Received Power (S-RSRP) as the reference measurement for the radio link quality of the synchronization source. S-RSRP is measured on the DMRS of PSBCH, which is only transmitted by D2D synchronization source. For Network-to-UE discovery, a new reference measurement of radio link quality (RLQ) needs to be defined without changing the hardware in the D2D device.